Process of treating cellulosic material



atented Dec. 2, 1930 UNITED STATES PATENT OFFICE- OAMILLE DREYFUS, OF NEW YORK, N. Y., AND GEORGE SCHNEIDER, OF CUMBERLAND, MARYLAND, ASSIGNORS TO CELANESE CORPORATION OF AMERICA, A CORPORATION OF DELAWARE PROCESS OF TREATING CELLULOSIC MATERIAL No Drawing.

This invention relates to a process for the treatment ofcellulosic materials whereby such material is rendered suitable for esterifica-- tion. 'The usual method of esterifying cellulosic materials consists in treating said matefatty acid, usually, but not necessarily, the one correspondingto the ester desired.

It has been found, when operating according to the methods above indicated, that certain cellulosic materials yield very poor re-. sults. This has been explained on the ground that such cellulosic materials are more or less inactive or resistant toward esterification. Also it has been heretofore diflicult to produce suitable higher fatty acid esters of cellulose,

such as cellulose butyrate and cellulose propionate even when a so-called very reac tive cellulose is employed (by a reactive cellulose We means a cellulose which very readily forms an ester of a low fattyacid,

such as cellulose acetate or formate) Also in these processes (using inactive cellulose or in the manufacture of cellulose butyrate or cellulose propionate) it has been observed that zinc chloride and strong acids such as the phosphoric acids which should be good catalysts do not act as such unless high temperatures are employed. Under such temperature conditions while esters are obtained, they are mostly of practically no commercial value because of the resultant degradation of the cellulose molecule.

An object of this invention is to render inactive cellulosic material suitable for esterification. Another object is to commercially and economically prepare the more difiicultly manufactured fatty acid esters of cellulose. Still another object is to utilize the now unused strong acids such as the phosphoric acids as catalysts for the esterification of cellulose,

whereby the fatty acid esters of cellulose may he obtainedwith minimum degradation of the cellulose molecule. Yet another object of our invention is to produce fatty acid esters of cellulose of excellent quality and high commercial value. Still another object of this Application filed March 12, 1927. Serial No. 175,004.

invention is to devise a process for producing these products in an economical and expeditious manner. Other objects and advantages of the invention will appear in the detailed description of the invention.

Samples of active and inactive cotton were examined and the only differences which could be detected microscopically were striations on the surface of the inactive cotton. These striations indicated that the cotton had been over-treated in the bleaching and/ or the purification treatments. These striations are due to a hardening and contraction of the surfade, producing a much denser layer of material on the surface. This tough outer layer explains the resistance of such coated material to the usual esterification treatments.

The degree or extent of these striations in- 'dicates the ease (or difficulty) with which the material can be esterified when subjected to the usual .esterifying processes. That is, this peculiar condition of the outer surface of the cotton accounts for or explains the variable activity of the different samples of cotton, preventing, as it does, the desired penetration of the esterifying solution into the cotton. Where the cellulosic material is tubular in structure this hard and dense condition exists on the inner surfaces as Well as on the outer surfaces.

Methods of activation employed today have serious draw-backs. Among the more important is the fact that they do not result in complete or uniform activation, and therefore, make it impossible to obtain homogeneous esterification of the cellulose. Also the known activating processes necessitate the use of bulky, cumbersome and expensive apparatus.

Our invention overcomes these and other difliculties. We have discovered that uniform and excellent activation of the cellulose material can be obtained by first subjecting the cellulose material to complete evacuation or vacuum and then introducing a vaporized fatty acid such as acetic acid into the cellulosic material. Because of the evacuation, the acetic acid vapors enter into the interstices of the material which formerly enclosed air, so that a degree of activation is achieved far superior to any heretofore known. We do not know what the mechanism of this reaction is but this superior activation is probably attributable to the softening of all the harder and denser portions of the material by the acid vapors. However, we do not desire to be bound by this explanation as the increased activity may be due to other causes. This softening allows thorough penetration of the mass of cellulosic material by the esterifying solution, with correspondingly improved results.

We found that esterifying a normally active cellulose which had first been pretreated or activated as above set out yielded excellent results. Not only was the esterification much more complete than usual but it was accomplished in half the time usually consumed in the reaction. In addition to the above economical advantages the products obtained possess superior qualities over the products obtained from the usual esterification processess, since they are uniform and are obtained with less degradation of the cellulose molecule.

Normally active cellulose was subjected to esterification processes for the production of cellulose butyrate and propionate. Only a slight esterification of the cellulose resulted. Some of the cellulose material was then pretreated in accordance with the present invention, that is, under vacuum with the vapors of a fatty acid, preferably acetic acid, and then subjected to the usual esterification reactions. The thus pretreated material was found to esterify very readily, yielding cellulose butyrate and propionate of excellent quality.

Substances such as zinc chloride, phosphoric acids, etc., should normally act as good catalysts for the esterification of cellulose but great difliculty has been met with in their employment in commercial processes. We have now found that if the cellulosic material is pretreated in accordance with the present invention that these substances will act as excellent catalysts in the esterification of the pretreated cellulosic material even though the reaction is carried on at a comparatively low temperature.

As an example of a method of activating cellulosic material in accordance with our invention we may proceed as follows: 100 parts of purified cellulose (cotton linters, purified wood-pulp etc.) are placed in a receptacle and the latter evacuated. While the receptacle is under vacuum, 5 to 20 parts of glacial acetic acid, which has been previously heated to its boiling point in a separate container, are introduced into the receptacle through a suitable connection. The hot acid vaporizes as soon as it enters the receptacle and in this vaporized condition enters the cells, tubes, pores and interstices of the cellulose. The amount of acid introduced into the receptacle can be varied over a very wide range, the amount added determining the extent to which the vacuum existing in the receptacle is satisfied or reduced. Where desired, an amount of acid can be added sufficient to completely satisfy the vacuum or preferably the amount of acid added may be so regulated that after the same has vaporized in the receptacle there will still be a slight vacuum existing in the a paratus.

After the requisite amount of acetic acid has been added, it is permitted to act upon the cellulose, in the ti htly closed container, for approximately 1 hour or until the de sired activation is obtained. At the end of this time an examination of the cellulose shows that all of the hardened portions of the same have been softened, as previously described, by the action of the acid vapors. The cellulosic material can now be subjected to the usual esterification reaction. Where desired, this esterification may be carried on in the same receptacle in which the pretreatment of the cellulose has been effected or the material may be transferred from the pretreatment apparatus to the esterifying machine.

The above example is not to be considered limitative as it sets out but one method of carrying out the applicants invention. Thus .cellulosic material may be extended, or even curtailed, depending upon the condition of the cellulose being treated. The more inactive the cellulose the greater the time necessary for the activation of this material.

Cellulosie materials usually employed for the manufacture of cellulose esters must conform to rigid specifications since not all grades of cellulose will yield commercially valuable cellulose esters, in fact some grades of cellulose will not even esterify to any appreciable extent. Thisobjectionable feature of cellulosic materials is overcome when the cellulosic material is first activated in accordance with the present invention. This pretreatment has made it possible to produce commercially valuable esters of cellulose even when a grade of cellulose was used which is not ordinarily esterifiable when subjected to the usual esterification processes. The" esters obtained from'different grades of cellulosic material which had been pretreated in accordance with this invention were found to be uni form and excellent in quality.

it will, therefore, be seen that as a result of the applicants invent-ion not only is it .cellulose esters but these are obtained in a 7 short time and with simpler apparatus than has been necessary heretofore. Also where desirable, the pretreated cellulosic material may be esterified without any handling after the activation, as the esterification can be et fected in the apparatus used for the activation of the material. The cellulose molecule is consequently less degraded and yields esters of higher viscosities.

Having described our invention what we claim and desire to secure by Letters Patent 1s:

1. A process of treating cellulosic material which consists in subjecting the cellulosic material to a high degree of vacuum, introducing int-o the cellulosic material, while the same is under reduced pressure, a heated lower fatty acid and allowing the acid to act upon the cellulosic material until all portions of the latter are in suitable condition for esterification.

2. Aprocess of activating cellulosic material which comprises subjecting the cellulosic materialto a high degree of evacuation, adding to the cellulosic material, while the latter is under a vacuum, a lower fatty acid which has been heated to its boiling point and allowing the introduced acid to act upon the cellulosic material for approximately one hour.

3. A process of treating cellulosic material which consists in introducing the cellulosic material into an air-tight container, evacuating said container, introducing into the container a lower fatty acid heated approximately to its boiling point, the amount of acid added being insuficient to completely satisfy the vacuum, and permitting the introduced acid to act upon the cellulosic material for approximately one hour.

4. A process of treating cellulosic material which consists in subjecting the cellulosic material to a high degree of vacuum, introducing into the cellulosic material, while the same is under reduced pressure, heated glacial acetic acid and allowlng the acid to act upon the cellulosic material until all portions of the latter'are in an activated condition.

5. A process of activating cellulosic matewhich consists in introducing the cellulosic material into an air-tight container, evacuating said container, introducin into the container glacial acetic acid heate approximately to its boiling point, the amount of acid added being insufiicient to completely satisfy the vacuum and permitting the acid to act upon the cellulosic material for approximately one hour.

7. A process of treating cellulosic material which comprises placing 100 parts of purified cellulose in an air-tight receptacle, completely evacuating said receptacle, introducin into said receptacle five (5) to twenty (20 parts of glacial acetic acid previously heated to approximately its boiling point, allowing the acetic acid to act upon the cellulosic material in said receptacle until activation is obtained.

8. A process of treating cellulosic material which comprises placing 100 parts of purified cellulose in an air-tight receptacle, completely evacuating said receptacle, introducin into said receptacle five (5) to twent (20 parts of glacial acetic acid previously eated to approximately its boiling point, allowing the acetic acid to act upon the cellulosic material for approximately one hour.

In testimony whereof, they have hereunto subscribed their names.

CAMILLE DREYFUS. GEORGE SCHNEIDER. 

